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Atomic-layered Au clusters on α-MoC as catalysts for the low-temperature water-gas shift reaction

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Science  28 Jul 2017:
Vol. 357, Issue 6349, pp. 389-393
DOI: 10.1126/science.aah4321
  • Fig. 1 Catalytic properties and structural characterization of the (2%)Au/α-MoC catalyst.

    (A) In situ XRD (wavelength, 0.3196 Å) of the (2%)Au/α-MoC catalyst under WGS reaction conditions at various temperatures. The y axes in the top and bottom panels are in arbitrary units. The rainbow color scheme in the middle panel spans from no signal (blue) to high-intensity diffraction peaks (red). MoO2 and α-MoC are shown on the right as ball-and-stick diagrams (red, O; purple, Mo; black, C). (B) CO conversion on different catalysts at various temperatures (10.5% CO/21% H2O/20% N2 in Ar; GHSV, 180,000 hour−1). (0.9%)Au/α-MoC was produced by NaCN leaching of (2%)Au/α-MoC. (C) The activity of different catalysts (moles of CO per moles of metal per second), measured at CO conversion below 15% in 11% CO/26% H2O/26% H2/7% CO2/30% N2. (D) Kinetic orders (n) of the reactants and products. (E) Apparent activation energy Eapp of various catalysts in 10.5% CO/21% H2O/20% N2-Ar balance.

  • Fig. 2 Mechanism study and electron microscopy characterization.

    Water adsorption (at 303 K) followed by CO TPSR, using (A) (2%)Au/α-MoC, (B) α-MoC, and (C) (2%)Au/SiO2. Signals of H2 [mass/charge (m/z) = 2], H2O (m/z = 18), CO (m/z = 28), and CO2 (m/z = 44) were detected. (D and E) High-resolution high-angle annular dark-field (HAADF)–STEM images of fresh (2%)Au/α-MoC, with single atoms of Au marked in blue circles and layered Au structures highlighted in yellow. The Au clusters were further identified by elemental analysis (figs. S18 and S19). (F) HAADF-STEM image of the (2%)Au/α-MoC catalyst after reaction, in which the sample still contains both single-atom Au and layered Au clusters. (G) HAADF-STEM image of the (2%)Au/α-MoC catalyst after NaCN leaching, showing predominantly single atoms of Au, most of which overlap with Mo sites in the support lattice. The very bright features in this image are caused by overlapping MoC particles, as confirmed by elemental mapping (figs. S18 and S19).

  • Fig. 3 The reaction paths for the WGS reaction on Au15/α-MoC(111).

    (A) H2O dissociation and CO reforming at lower coverage, (B) O-assisted H2O dissociation on the boundary oxidized by three O atoms, and (C) CO reforming at high coverage. The energies of gaseous molecules include the zero-point energy and entropy correction at 423 K. Au, Mo, C, O, and H atoms are shown in gold, cyan, gray, red, and white, respectively; to distinguish the C atom in CO, it is represented in black. The subscripts (g), b, and t denote gas phase, bridge site, and top site, respectively. TS, transition state.

  • Table 1 Comparison of the activities of the representative catalytic systems for the low-temperature WGS reaction.

    The operating pressure of the reactions was 1 bar.

    Temperature
    (kelvin)
    Gas feed
    composition
    Mass-specific
    activity (micromoles
    of CO per grams
    of catalyst
    per second)
    Metal-normalized
    activity (moles
    of CO per
    moles of metal
    per second)
    Apparent
    activation
    energy
    (kilojoules
    per mole)
    Reference
    Reducible oxide supports
    Au/CeO252311% CO/26% H2O/26% H2/7% CO2 in He4.80.1337 (1)
    Pt/CeO252311% CO/26% H2O/26% H2/7% CO2 in He220.1775 (1)
    Ir1/FeOx5732% CO/10% H2O in He1.22.3250 (21)
    Au/FeOx59811% CO/26% H2O/26% H2/7% CO2 in He110.3149 (22)
    Alkali-promoted inert supports
    Au-Na/MCM4142311% CO/26% H2O/26% H2/7% CO2 in He0.80.06744 (5)
    Pt-Na/SiO252311% CO/26% H2O/26% H2/7% CO2 in He120.2470 (4)
    Pt-Na/CNT4732% CO/10% H2O in He1.250.02470 (23)
    Molybdenum carbide supports (β-Mo2C)
    Pt/Mo2C51311% CO/ 21% H2O/43% H2/6% CO2 in N22211.4253 (11)
    Pt/Mo2C3937% CO/22% H2O/37% H2/8.5% CO2 in Ar1.80.02348 (12)
    Au/Mo2C3937% CO/22% H2O/37% H2/8.5% CO2 in Ar1.60.02144 (12)
    Homogeneous catalysts
    Ru3(CO)123731 bar CO, NaOH solution0.122.6 × 10–5no data (24)
    Our results
    (2%)Au/α-MoC3133% CO/6% H2O/ 20% N2 in Ar1.220.012
    3335% CO/10% H2O/20% N2 in Ar5.910.06
    35313.060.13
    39310.5% CO/21% H2O/20% N2 in Ar1031.05
    4231671.6622*
    4733253.19
    (2%)Au/α-MoC3335% CO/10% H2O/10% H2/3% CO2 in N22.390.02
    3539.200.09
    39311% CO/26% H2O/26% H2/7% CO2 in N2530.62
    4231061.0527
    4732132.02
    (0.9%)Au/α-MoC
    (leached by NaCN)
    39310.5% CO/21% H2O/20% N2 in Ar9.070.09
    42326.60.2641
    47373.10.72
    (2%)Au/β-Mo2C39311% CO/26% H2O/26% H2/7% CO2 in N22.060.02
    4234.290.0438
    47314.40.14
    α-MoC39311% CO/26% H2O/26% H2/7% CO2 in N22.05
    4238.57 64
    47356.7
    (2%)Au/SiO267310.5% CO/21% H2O/20% N2 in Ar0.242.4 × 10–3
    (2%)Au/CeO242311% CO/26% H2O/26% H2/7% CO2 in N21.10.01

    *The activation energy was also determined by another method (fig. S17).

    Supplementary Materials

    • Atomic-layered Au clusters on α-MoC as catalysts for the low-temperature water-gas shift reaction

      Siyu Yao, Xiao Zhang, Wu Zhou, Rui Gao, Wenqian Xu, Yifan Ye, Lili Lin, Xiaodong Wen, Ping Liu, Bingbing Chen, Ethan Crumlin, Jinghua Guo, Zhijun Zuo, Weizhen Li, Jinglin Xie, Li Lu, Christopher J. Kiely, Lin Gu, Chuan Shi, José A. Rodriguez, Ding Ma

      Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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      • Materials and Methods
      • Supplementary Text
      • Figs. S1 to S32
      • Tables S1 and S5
      • References

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